Surface Technology

Research project

Basic chemicals and carbon from old bakery products

In Germany, up to 100,000 tonnes of old bakery products accumulate every year which are not suitable for human consumption or as animal fodder. Until now, their use has been primarily energetic, for example in combustion processes or in biogas plants. In this project, we are developing a process for the material recycling of regionally available old bakery products which will enable them to be used as a basis for the production of bioplastics for the chemical industry. A carbonaceous substance with an attractive calorific value is thereby generated as a by-product.

The left section of the image shows a pile of old bakery products. To the right of this are a spoon with a dark brown powder, a spoon with pale brown lumps, a small glass bowl with brown liquid and a small glass bowl with white liquid.
© Fraunhofer WKI | Manuela Lingnau
A special process is used to produce the basic chemical hydroxymethylfurfural (shown here both as a brown aqueous solution and as a brownish solid) and carbon (shown here in powder form) from old bakery products. HMF can be further processed to create, amongst other things, polyester resins. These can be used to produce aqueous polyurethane dispersions (white liquid).
The illustration shows four different extraction methods using methylisobutylketone and chloroform, once with and once without prior saturation with sodium chloride. The accompanying diagram shows the quantity of hydroxymethylfurfural extracted per extraction cycle and extraction method. Five extraction cycles were performed.
© Foto Fraunhofer WKI | Steven Eschig
The quantity of hydroxymethylfurfural extracted depends on the selected extraction method and the number of extraction cycles.
Response profile for the production of HMF from glucose, showing the chemical structural formulae (Natta projection).
© Fraunhofer WKI | Steven Eschig
The starch from the old bakery products is converted into glucose and then into fructose. The fructose reacts further to form hydroxymethylfurfural through gradual dehydration.

Our research approach is to extract the basic chemical hydroxymethylfurfural (HMF) and carbon from old bakery products such as bread, rolls and cakes. As a versatile starting material for the production of bioplastics, HMF plays a key role in the development of a bio-based economy (bioeconomy). At present, HMF is primarily extracted from fructose and therefore competes against food production. Old bakery products, in contrast, offer an excellent non-food source. According to EU Directive 1774/2002, food waste must not be fed to livestock. Whilst the feeding of old bread and pasta products would still theoretically be possible, ensuring the varietal purity is extremely laborious and is therefore hardly ever practiced.

The project team at the University of Hohenheim is developing a process for the hydrothermal treatment of old bakery products. The starch contained in large quantities in the old bakery products is thereby converted into HMF in aqueous solution and carbon. The process parameters (pH value, temperature, duration) are selected in such a way as to achieve the highest possible yields of HMF.

Carbon is produced as a by-product of the hydrothermal treatment. It can be used as a biofuel or as soil fertilizer. Simultaneously, it is a good adsorbent. Our project partners at the University of Hohenheim will investigate whether it is possible to use the carbon as an adsorption filter to isolate HMF from the aqueous solution.

In addition, at the Fraunhofer WKI, we are investigating extractive methods for the isolation of HMF from the aqueous phase. Both methods will be evaluated with respect to their economic efficiency. The aim is to reduce the use of solvents for the isolation of HMF to a minimum.

In cooperation with the University of Hohenheim and our industrial partner, we ultimately combine the individual processes “hydrothermal pre-treatment” and “isolation” to form an overall process and to transfer it to a semi-industrial scale. In further laboratory tests at the Fraunhofer WKI, we will synthesize the first polymers from the obtained HMF and will examine them with regard to their application possibilities.

Bioplastics on the basis of furan derivatives such as HMF offer a number of unique technical features which cannot be easily achieved with other biopolymers. These include improved hardness and scratch-resistance as well as the possibility of synthesizing self-healing polymers. The potential of plastics which are based on furan can be clearly seen in polyethylene furanoate (PEF), which has already been extensively investigated. This material can be used, for example, to produce reusable bioplastic bottles - as a sustainable alternative to the PET bottles commonly used up until now.

The conversion of regionally available old bakery products into high-quality bioplastics will save fossil resources and reduce transportation distances. The fact that carbon is thereby generated as a by-product, which can be used either as a biofuel or soil fertilizer, makes the material recycling of old bakery products additionally attractive.

Project partner

  • University of Hohenheim


Funding body: German Federal Ministry of Education and Research (BMBF)

Project management: Project Management Jülich (PtJ)

Funding reference: 031B0488C

Duration: 1.9.2018 to 31.8.2020